The invention relates generally to metal-cored weld wires, and more specifically to metal-core weld wires usable for gas shielded arc welding low carbon and low alloy galvanized and galvannealed steels at relatively high weld rates to produce improved weld deposits on overlapping or butted workpieces with no gap therebetween.
In many gas shielded arc welding applications, low carbon and low alloy galvanized and galvannealed steels are welded in single pass, high weld rate operations that require weld deposits on gapless joints with minimum hot cracking, minimum blow hole formation and substantially no porosity, minimum slag formation and spatter, good wetting characteristic and corrosion resistance, no liquid metal embrittlement, improved impact strength, and a minimum tensile strength of approximately 85,000 psi.
Galvanized steels are formed by coating or depositing zinc on steel in a hot dipping, or a sherardizing, or an electroplating process. The galvanized metal is sometimes annealed to form a galvannealed metal with improved properties including reduced flaking of the coating, which tends to occur during metal forming operations. When welding galvanized and galvannealed metals, however, there is a tendency for zinc vapor to enter into the molten weld pool, which results in a defective weld deposit. More specifically, zinc coating vaporized from the surface of the metal tends to create turbulence in the shielding gas thereby introducing atmospheric nitrogen and oxygen into the weld pool resulting in nitrogen and oxygen contamination of the weld deposit and increased spatter. In addition, zinc vapor is not readily soluble in molten steel, and any vapor that does not escape from the molten weld pool before solidification results in the formation of blow holes and pores in the weld deposit. Blow hole and pore formation are particularly severe when welding joints without a gap between the workpieces since there is limited area for vapor to escape from the molten weld pool.
Galvanized metals are known for improved corrosion resistance, and are used increasingly in the automotive industry for automobile frames, bumpers, axles, cradle assemblies, fenders, and water heaters among other components, which often require welding gapless joints. These metals are generally low carbon and low alloy steels having good press forming characteristics. In some applications, industry uses low carbon and low alloy galvannealed steels with a thickness ranging between approximately 0.030 and 0.250 inches and a coating weight of approximately 45 gm/m.sup.2. The relatively thin gauge steels often must be welded in a single pass at high weld rates to prevent the welding arc from burning through the metal. Assembly line operations also require single pass, high weld rates to improve productivity. Weld rates up to approximately 150 cm/min are sometimes required. At high weld rates, however, the molten weld pool tends to cool relatively rapidly thereby reducing the time for vapor to escape from the weld pool, which increases the formation of blow holes and porosity in the weld deposit. The rapidly cooled weld deposit formed in high weld rates applications tends also to result in a poor weld deposit contour, or wetting characteristic. High weld rates are also a source of turbulence in the shielding gas, which tends to increase the addition of atmospheric nitrogen and oxygen into the weld pool as discussed above.
Presently, galvanized steels are welded with self shielded weld wires containing magnesium and barium. The magnesium displaces nitrogen and oxygen to reduce porosity. But the magnesium also reacts with the zinc coating to cause liquid metal embrittlement, which is unacceptable in many industrial applications. These self shielded wires also produce excessive smoke, which is undesirable, and moreover produce excessive spatter and slag, which must be removed before applying coatings over the weld deposit. Slag formation tends also to prevent vapor from escaping from the molten weld pool resulting in increased blow holes and porosity, which are further increased when welding gapless joints. In addition, barium is considered toxic and creates an unacceptable health hazard.
JP Patent Application No. 61-21432 discusses a solid weld wire for gas shielded arc welding galvanized steels. Solid wires, however, have undesirable deep "finger" penetration and reduced productivity in comparison to metal-core wires. In addition, the solid weld wire of JP Patent Application No. 61-21432 has a relatively high carbon content, which may reduce ductility and increase hot cracking sensitivity and spatter. This solid weld wire also has a relatively high titanium content, which increases slag formation, and includes aluminum, which increases spatter and provides a poor wetting characteristic. The solid weld wire of JP Patent Application No. 61-21432 therefore tends to be expensive and is not suitable for welding at high weld rates.
JP Patent Application No. 1989-3833 discusses a solid weld wire for gas shielded arc welding galvanized steels at high weld rates. JP Patent Application No. 1989-3833, however, teaches that it is undesirable to add aluminum, titanium, silicon and other deoxidizing agents to the solid weld wire because deoxidizing agents allegedly increase the activity of zinc in the molten weld pool resulting in blow hole formation. The solid weld wire of the JP Patent Application No. 1989-3833 also produces slag resulting possibly from the substantial elimination of deoxidizing agents from the weld wire. The solid weld wire of the JP Patent Application No. 1989-3833 includes niobium and vanadium to reduce blow hole and pore formation in cases where gas shielding effectiveness is reduced. The amounts of niobium and vanadium disclosed in JP Patent Application No. 1989-3833, however, result in increased hot cracking and have an adverse affect on ductility. In addition, this solid wire has increased strength and hardenability that results in increased loads on wire drawing dies during manufacture of the weld wire increasing production costs.
In view of the discussion above, there exists a demonstrated need for an advancement in the art of metal-core weld wires.
It is therefore an object of the invention to provide a novel metal-core weld wire that overcomes problems with the prior art.
It is also an object of the invention to provide a novel metal-core weld wire usable for gas shielded arc welding low carbon and low alloy galvanized and galvanealed steels at relatively high weld rates to produce improved weld deposits on joints with no gap therebetween.
It is another object of the invention to provide a novel a metal-core weld wire usable for gas shielded arc welding relatively thin gauge low alloy and low carbon galvanized and galvanealed steel at relatively high weld rates.
It is another object of the invention to provide a novel a metal-core weld wire usable for gas shielded arc welding low alloy and low carbon galvanized and galvanealed steels at weld rates up to 150 cm/min wherein the weld deposit has reduced blow hole and pore formation, no liquid metal embrittlement or hot cracking, improved weld deposit wetting characteristic, improved impact strength and ductility, and improved corrosion resistance, at relatively high weld deposit rates.
It is yet another object of the invention to provide a novel metal-core weld wire usable for gas shielded arc welding low alloy and low carbon galvanized and galvanealed steels wherein the metal-core weld wire produces reduced arc ionization potential, reduced spatter, and improved shielding at relatively high weld deposit rates.
Accordingly, the invention is drawn to a metal-core weld wire usable for gas shielded arc welding low carbon and low alloy galvanized and galvanealed steels. The metal-core weld wire includes a low carbon steel sheath surrounding a core composition. In one embodiment, the low carbon steel sheath includes, by total weight of the metal-core weld wire, between approximately 0.01-0.03% C, and the core composition includes, by total weight of the metal-core weld wire, between approximately 0.05-0.20% Ti and between approximately 0.05-1.00% Nb, wherein the metal-core weld wire includes between approximately 0.40-0.50% Si. In one embodiment, the core composition includes Mn to the extent that the metal-core weld wire includes between approximately 0.1-1.0% Mn, and iron powder. The core composition may also include, by total weight of the metal-core weld wire, between approximately 0.02-1.00% Cu, and in another embodiment between approximately 0.05-0.80% V. The core composition is, by total weight of the metal-core weld wire, between approximately 0.001-12.0%, and in an alternative embodiment between approximately 5.0 and 7.0%. The weld wire provides, at weld rates up to 150 cm/min, reduced arc ionization potential and spatter, and improved arc stability and shielding. The weld wire produces, at weld rates up to 150 cm/min, weld deposits having reduced blow holes and porosity, no liquid metal embrittlement, improved corrosion resistance and ductility, and reduced weld pool surface tension resulting in an improved wetting characteristic when welding gapless joints.
These and other objects, features and advantages of the present invention will become more fully apparent upon consideration of the following Detailed Description of the Invention with the accompanying drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced by corresponding numerals and indicators.